You need to configure the Network Security Group that is associated with subnet0.
In the Azure portal, type Virtual Networks in the search box, select Virtual Networks from the search results then select VNET1. Alternatively, browse to Virtual Networks in the left navigation pane.
In the properties of VNET1, click on Subnets. This will display the subnets in VNET1 and the Network Security Group associated to each subnet. Note the name of the Network Security Group associated to Subnet0.
Type Network Security Groups into the search box and select the Network Security Group associated with Subnet0.
In the properties of the Network Security Group, click on Inbound Security Rules.
Click the Add button to add a new rule.
In the Source field, select Service Tag.
In the Source Service Tag field, select Internet.
Leave the Source port ranges and Destination field as the default values (* and All).
In the Destination port ranges field, enter 7777.
Change the Protocol to TCP.
Leave the Action option as Allow.
Change the Priority to 100.
Change the Name from the default Port_8080 to something more descriptive such as Allow_TCP_7777_from_Internet. The name cannot contain spaces.
Click the Add button to save the new rule.

Reference:
https://github.com/MicrosoftDocs/azure-docs/blob/master/articles/security-center/custom-security-policies.md
https://zimmergren.net/create-custom-security-center-recommendation-with-azure-policy/

This is a tricky one because uploading a certificate is also required. However, the question states that the Token Encryption option is unavailable. This is because the app is not added as an enterprise application. When the app is added as an enterprise application, the Token Encryption option will be available. Then you can upload the certificate.
Reference:
https://docs.microsoft.com/en-us/azure/active-directory/manage-apps/howto-saml-token-encryption