Troubleshooting

This plugin provides a log debugging tool to help you monitor what happens during membership checkout and when payments are processed in the background.

If you experience any problems, you can turn on WordPress debug mode and find the log file in your hosting's wp-content/ folder. The log files start with nowpayments, such as nowpayments-df897a8544b63a422b03736ab33be7d4.log

Read Debugging in WordPress https://developer.wordpress.org/advanced-administration/debug/debug-wordpress/