Looking at the source code, I found that it was caused by the absence of $slot.

Solution:

Enable the component2 compilation mode of Alipay applet.

Enabling method:

1. In the project development interface of Alipay applet development tool, click the “File” menu-click “Project Details”, and in the “Details” tab content that opens in the middle, check the “Enable component2 compilation” item under the “Project Configuration” item Item.

2. If it is a uni-app project, open the manifest.json file, select the source view, and find the “mp-alipay” item. If you don’t add it yourself, add “component2”: true, as follows:

“mp-alipay”: {
“usingComponents”: true,
“component2”: true
},