Man pages matching name gnutls_srp_base64_decode2 in section 3:

gnutls_srp_base64_decode2.3.en	debian 10 / gnutls-doc
gnutls_srp_base64_decode2.3.en	debian 11 / gnutls-doc
gnutls_srp_base64_decode2.3.en	debian 12 / gnutls-doc