When there is an error in AMP page, Google search console will display issues for your site by sending a notification in the form of email about the AMP Issues. Once you log into Google Search console, you may be able to see which AMP pages are having issues as shown below..(Most of the AMP pages might have similar issues, so the fix might be an easy one)
When you click on any of the errors above, it will show the list of pages that has an issue under Examples and clicking on any page will display the error as shown in the below screenshot
There are 2 ways to troubleshoot for issues, one is to use Google’s AMP Validator or copy the code from right pane and following the below steps to validate by code wise.
Step 1: Copy the code on the right pane
Step 2: Go to https://validator.ampproject.org/
Step 3: Paste the code directly in the box given and as soon as you paste the code, it would display errors as shown below
Step 4: Click on any of the errors and it will show where exactly the issue and under which tag. Like this click on each error will display where exactly the error and what should be remediation done to fix the issue..
Apart from this, there is also another way which you can test an AMP page by using Google’s AMP validator.