AppSheet provides several ways to integrate with external web services.
AppSheet Rest API [Inbound]
External web services can invoke the AppSheet Rest API to access a table within an AppSheet app. The external web service can Add, Delete, Edit (update), Find (read), or Invoke a pre-defined Action in the app. You can learn more about the Rest API here.
AppSheet Workflow Webhooks [Outbound]
The basic verbs are Delete, Patch, Post and Put. There is no return nor expectation of one by design. A variety of API body payloads and header configurations are supported.
Note: currently there is no multipart file upload (e.g. base64 image) mime type support.
Direct connect to oData protocol [Inbound]
AppSheet can directly connect to oData sources. If your Rest API is represented as an oData feed this is a zero effort experience. You can learn more here.
Direct connect to external Rest API (Apigee) [Inbound]
AppSheet can connect to Rest API endpoints which meet certain requirements, e.g. can be represented as an OpenAPI Spec (swagger) or can be exposed in such a way that they are one or more rectangular or tabular data sources. More information is available here
You can use an AppSheet webhook to trigger a Zappier Zap. The Zappier Zap can, in turn, access hundreds of external services. You can learn more here.
You can create a Zappier Zap that invokes the AppSheet REST API. You can use the REST API to Add, Update, Delete, and Find (read) records in an AppSheet table. You can also use the REST API to invoke a pre-defined AppSheet Action. You can learn more here.