The catalog entry should be also be updated to remove the unecessary email field DNSimple Email Address and indicate which DNSimple token to use (there are at least 3 different possibilities only one of which works):
Replace:
DNSSimple API Key
Enter your DNSimple API key.
by
DNSImple Account Access token (API v2)
Enter your DNSImple Account Access token (API v2).
The catalog entry should be also be updated to remove the unecessary email field
DNSimple Email Address
and indicate which DNSimple token to use (there are at least 3 different possibilities only one of which works): Replace:by