If you run into an error after onboarding with not being able to access APX 2.0 it could be due to your setup not accepting the ciphers needed in order for our APX application to run properly. Please see the details below.
The payments-api.abacusnext.com endpoint currently only accepts these four cipher suites, and only with TLS v1.2:
TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 (dh 2048)
TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 (dh 2048)
All four of these cipher suites are on the current list of acceptable cipher suites for RSA certificates as per NIST Guidelines (See here on page 17).