Shifter supports AMP with "AMP for WordPress" plugin By WordPress.com VIP, XWP, Google, and contributors, and doesn't support any other AMP generator plugins like AMP for WP – Accelerated Mobile Pages or Better AMP.
It means if you enabled unsupported AMP plugin and generated your site, AMP pages will not generate.
Please use "AMP for WordPress" plugin instead of the alternatives.
AMP Settings
Template Mode
Choose: Reader
The latest version of AMP plugin supports three modes, Standard, Transitional and Reader. If your theme supports AMP, we recommend to select the Reader.
Reader theme
Choose AMP Legacy
Supported Template
Check on Posts, Pages, Media as you like.
Shifter currently supports only Posts, Pages and Media.
Advanced Settings
Redirect mobile visotors to AMP
Turn off this feature, Shifter currently doesn't support it.
Plugin Suppression
Set as you like.
Analytics (optional)
You can set Analytics code such as Google Universal Analytics.
Refer to official document Analytics Vendors to check your vendor is supported.
The analytics code should be JSON format. Refer amp-analytics and Analytics document for more details.
Note
AMP pages on Shifter should be end with /amp/.
For example,
Normal posts/pages:
https://example.com/this-is-test/AMP posts/pages:
https://example.com/this-is-test/amp/