Magento what a freaken NIGHTMARE working with this cms.
Anyways lets get started.
https://support.magento.com/hc/en-us/articles/360024368392-Update-Authorize-Net-Direct-Post-from-MD5...
This didn't work for me
had upgrade from 2.2.6 to 2.30 didn't use right pach
still getting this erro
fixed by php bin/magento setup:upgrade; php bin/magento setup:static-content:deploy -f;