Hello @Varden, welcome to the Let's Encrypt community. 
Seeing this makes me think likely you are redirecting http to https and your presently certificate being served is expired.
This online tool SSL Server Test (Powered by Qualys SSL Labs) is showing an expired certificate being served
SSL Server Test: www.arms-rol.org (Powered by Qualys SSL Labs)
This is the certificate I received
$ openssl s_client -showcerts -servername www.arms-rol.org -connect www.arms-rol.org:443 < /dev/null
CONNECTED(00000003)
depth=2 C = US, O = Internet Security Research Group, CN = ISRG Root X1
verify return:1
depth=1 C = US, O = Let's Encrypt, CN = R3
verify return:1
depth=0 CN = arms-rol.org
verify error:num=10:certificate has expired
notAfter=Jan 5 18:57:14 2023 GMT
verify return:1
depth=0 CN = arms-rol.org
notAfter=Jan 5 18:57:14 2023 GMT
verify return:1
---
Certificate chain
0 s:CN = arms-rol.org
i:C = US, O = Let's Encrypt, CN = R3
a:PKEY: rsaEncryption, 2048 (bit); sigalg: RSA-SHA256
v:NotBefore: Oct 7 18:57:15 2022 GMT; NotAfter: Jan 5 18:57:14 2023 GMT
-----BEGIN CERTIFICATE-----
MIIFMDCCBBigAwIBAgISBOYCmVttbcdniz3Yie+lN/fZMA0GCSqGSIb3DQEBCwUA
MDIxCzAJBgNVBAYTAlVTMRYwFAYDVQQKEw1MZXQncyBFbmNyeXB0MQswCQYDVQQD
EwJSMzAeFw0yMjEwMDcxODU3MTVaFw0yMzAxMDUxODU3MTRaMBcxFTATBgNVBAMT
DGFybXMtcm9sLm9yZzCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMlx
lu0IHL7XBXyi0ubTjFOs5vJ45ahvRmwGCKby+ff2bZwVt5Xv2yxicXfLW2l3SFc3
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HSUEFjAUBggrBgEFBQcDAQYIKwYBBQUHAwIwDAYDVR0TAQH/BAIwADAdBgNVHQ4E
FgQURWbwaj66Ci33qxzERLJbiw6T5w0wHwYDVR0jBBgwFoAUFC6zF7dYVsuuUAlA
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MA0GCSqGSIb3DQEBCwUAA4IBAQBVURgs9V4j0+4C2GjhKJDLSAS7Cff2ickfh7lu
kZIE9VoykPCUJMsoh4ka5FMoskv4AnTzF9gL/mvL0eqSoBchlDWe7W/uXPSmnTi0
W8olQ/FJs44eCXcDemEpVCZf9lG/Q7O0jyRrViVCRz8h4ZDju2ty1Pt5Ct4uLFL9
8k921Ev7sJE0aAQOEbUlbXSMZw1MYTmTmPC3EbEgmzOH5bcD8xr9qN+I+zyN7myE
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sbhgyGmqlk6GypKmppKzAEH1WvpwqY8PGMPrHqDvcHFBh7Uc
-----END CERTIFICATE-----
1 s:C = US, O = Let's Encrypt, CN = R3
i:C = US, O = Internet Security Research Group, CN = ISRG Root X1
a:PKEY: rsaEncryption, 2048 (bit); sigalg: RSA-SHA256
v:NotBefore: Sep 4 00:00:00 2020 GMT; NotAfter: Sep 15 16:00:00 2025 GMT
-----BEGIN CERTIFICATE-----
MIIFFjCCAv6gAwIBAgIRAJErCErPDBinU/bWLiWnX1owDQYJKoZIhvcNAQELBQAw
TzELMAkGA1UEBhMCVVMxKTAnBgNVBAoTIEludGVybmV0IFNlY3VyaXR5IFJlc2Vh
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WhcNMjUwOTE1MTYwMDAwWjAyMQswCQYDVQQGEwJVUzEWMBQGA1UEChMNTGV0J3Mg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gt8TAQEBMA0GCSqGSIb3DQEBCwUAA4ICAQCFyk5HPqP3hUSFvNVneLKYY611TR6W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-----END CERTIFICATE-----
2 s:C = US, O = Internet Security Research Group, CN = ISRG Root X1
i:O = Digital Signature Trust Co., CN = DST Root CA X3
a:PKEY: rsaEncryption, 4096 (bit); sigalg: RSA-SHA256
v:NotBefore: Jan 20 19:14:03 2021 GMT; NotAfter: Sep 30 18:14:03 2024 GMT
-----BEGIN CERTIFICATE-----
MIIFYDCCBEigAwIBAgIQQAF3ITfU6UK47naqPGQKtzANBgkqhkiG9w0BAQsFADA/
MSQwIgYDVQQKExtEaWdpdGFsIFNpZ25hdHVyZSBUcnVzdCBDby4xFzAVBgNVBAMT
DkRTVCBSb290IENBIFgzMB4XDTIxMDEyMDE5MTQwM1oXDTI0MDkzMDE4MTQwM1ow
TzELMAkGA1UEBhMCVVMxKTAnBgNVBAoTIEludGVybmV0IFNlY3VyaXR5IFJlc2Vh
cmNoIEdyb3VwMRUwEwYDVQQDEwxJU1JHIFJvb3QgWDEwggIiMA0GCSqGSIb3DQEB
AQUAA4ICDwAwggIKAoICAQCt6CRz9BQ385ueK1coHIe+3LffOJCMbjzmV6B493XC
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PRmP6zjzZN7IKw0KKP/32+IVQtQi0Cdd4Xn+GOdwiK1O5tmLOsbdJ1Fu/7xk9TND
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ATAwMC4GCCsGAQUFBwIBFiJodHRwOi8vY3BzLnJvb3QteDEubGV0c2VuY3J5cHQu
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U1RST09UQ0FYM0NSTC5jcmwwHQYDVR0OBBYEFHm0WeZ7tuXkAXOACIjIGlj26Ztu
MA0GCSqGSIb3DQEBCwUAA4IBAQAKcwBslm7/DlLQrt2M51oGrS+o44+/yQoDFVDC
5WxCu2+b9LRPwkSICHXM6webFGJueN7sJ7o5XPWioW5WlHAQU7G75K/QosMrAdSW
9MUgNTP52GE24HGNtLi1qoJFlcDyqSMo59ahy2cI2qBDLKobkx/J3vWraV0T9VuG
WCLKTVXkcGdtwlfFRjlBz4pYg1htmf5X6DYO8A4jqv2Il9DjXA6USbW1FzXSLr9O
he8Y4IWS6wY7bCkjCWDcRQJMEhg76fsO3txE+FiYruq9RUWhiF1myv4Q6W+CyBFC
Dfvp7OOGAN6dEOM4+qR9sdjoSYKEBpsr6GtPAQw4dy753ec5
-----END CERTIFICATE-----
---
Server certificate
subject=CN = arms-rol.org
issuer=C = US, O = Let's Encrypt, CN = R3
---
No client certificate CA names sent
Peer signing digest: SHA256
Peer signature type: RSA
Server Temp Key: ECDH, prime256v1, 256 bits
---
SSL handshake has read 4730 bytes and written 444 bytes
Verification error: certificate has expired
---
New, TLSv1.2, Cipher is ECDHE-RSA-AES256-GCM-SHA384
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
Protocol : TLSv1.2
Cipher : ECDHE-RSA-AES256-GCM-SHA384
Session-ID: A4D06C472FFE0AAF617D88FF3474D0F73F330F016F49F0BDAC82365EDE110223
Session-ID-ctx:
Master-Key: F0ED2F41A80856576425050F2D6AFE813BCFDB349F78C4D96E6A14AF2F9AA6BA0A792F83F2CB338A11B6BF89CC3735B9
PSK identity: None
PSK identity hint: None
SRP username: None
TLS session ticket lifetime hint: 300 (seconds)
TLS session ticket:
0000 - 82 7a 0b a4 bd 53 3b c5-bc e1 fa f0 a3 03 00 72 .z...S;........r
0010 - 33 fb 02 d4 b2 70 2c 71-6a 51 08 1d 67 5b 8f ac 3....p,qjQ..g[..
0020 - a2 2f 3b 3a 6e 23 e1 4e-8f fc 50 51 22 54 97 37 ./;:n#.N..PQ"T.7
0030 - b5 c4 f7 76 95 34 cb 89-15 0d 2d 64 74 31 d2 5a ...v.4....-dt1.Z
0040 - a3 f5 ce 70 08 56 36 0e-0c 4d 94 0f 7d 98 17 8e ...p.V6..M..}...
0050 - d9 da bd 80 38 8b 22 cc-d8 fc 6b 51 e0 23 fa f5 ....8."...kQ.#..
0060 - 08 0f 54 28 8c 50 0a 2a-fd 1e 4c cb 87 68 4a b1 ..T(.P.*..L..hJ.
0070 - 1c 79 88 de 20 0f 55 17-c8 dc f2 6f 42 54 53 73 .y.. .U....oBTSs
0080 - 08 0b 3c 7d 46 50 6d fd-46 95 ae 32 cd b1 c1 51 ..<}FPm.F..2...Q
0090 - 4b a7 d4 59 71 d6 e2 85-57 3c 98 a4 34 66 9a 29 K..Yq...W<..4f.)
00a0 - e0 ee ff 98 01 24 4c 0d-c3 27 ac 5b 4f f3 6a e9 .....$L..'.[O.j.
00b0 - f2 a3 ea ad 8f 3f 0e 70-63 5b 6a c9 df 8a a2 87 .....?.pc[j.....
00c0 - 93 c8 ca 7f af 56 46 3c-fd ab 4c ae 9c 3c 00 ad .....VF<..L..<..
Start Time: 1673282222
Timeout : 7200 (sec)
Verify return code: 10 (certificate has expired)
Extended master secret: no
---
DONE
Here is what I got with curl
$ curl -Ii http://www.arms-rol.org/.well-known/acme-challenge/sometestfile
HTTP/1.1 302 Found
Date: Mon, 09 Jan 2023 16:38:06 GMT
Server: Apache/2.4.25
Location: https://arms-rol.org/index.php
Content-Type: text/html; charset=iso-8859-1
That is an old version of Certbot see here for Certbot 2.1.0 Release