I would assume the username matching settings in the plugin are not correct but... you could probably just delete that plugin and install one of the other well-known saml plugins like "auth_saml2" - this plugin is also better known in the community here as a lot more people are using it, and it's supported by a Moodle Partner (full disclosure - I work for that Moodle partner.)
you have posted an error trace for a plugin "auth_mo_saml" that has not been officially published in the moodle.org plugins db - I assume you got it directly from the developer who wrote the plugin? - you will need to ask the developer for help as I don't expect many people here reading this forum will have ever seen that plugin.
I would assume the username matching settings in the plugin are not correct but... you could probably just delete that plugin and install one of the other well-known saml plugins like "auth_saml2" - this plugin is also better known in the community here as a lot more people are using it, and it's supported by a Moodle Partner (full disclosure - I work for that Moodle partner.)
I would assume the username matching settings in the plugin are not correct but... you could probably just delete that plugin and install one of the other well-known saml plugins like "auth_saml2" - this plugin is also better known in the community here as a lot more people are using it, and it's supported by a Moodle Partner (full disclosure - I work for that Moodle partner.)