I have 0.5.0 altapay/magento2-payment module installed via the composer without any overridden files on my project. I've checked the latest version of your module (which is 0.14.0 on this moment) and found the same code for the form.phtml template.
I've got this message trying to reach any of the Shipment View page.
I'm attaching the screenshot of the message.
Reproducing
Create any order -> create shipment
Go to admin panel Sales-> Shipment
Pick any of the created shipments.
You will see the message only in developer mode. In production mode you will get just a page without content.
I have 0.5.0 altapay/magento2-payment module installed via the composer without any overridden files on my project. I've checked the latest version of your module (which is 0.14.0 on this moment) and found the same code for the form.phtml template.
I've got this message trying to reach any of the Shipment View page. I'm attaching the screenshot of the message.
Reproducing
You will see the message only in developer mode. In production mode you will get just a page without content.