'Callout from triggers are currently not supported' error

Use @future Methods for Callouts

To invoke a callout from a trigger in Salesforce Apex, wrap the callout logic in a @future method with the callout=true annotation. The @future annotation (Apex Future Annotation) marks a method to run asynchronously, meaning the callout occurs after the triggering transaction has completed.

For example, define a global class named MyClass with a static method annotated @future(callout=true). Inside that method, include the long-running Apex callout code. The annotation takes the format: @future (callout=true), followed by a public static void method that accepts serializable parameters such as Strings or primitive types.

global class MyClass {
     @future (callout=true)
     Public static void myMethod(String a)
     {
          //long-running Apex code
     }
}

Note: This approach only works if your required operation can be performed asynchronously, since @future methods do not return values to the triggering transaction.

Governor Limits for @future Methods

Future methods are subject to the following Apex governor limits:

• Maximum SOQL queries per future method invocation: 200

• Maximum heap size per future method invocation: 12 MB

• Maximum @future method calls per Apex invocation: 50

• Organization-wide limit on asynchronous method invocations (including Batch Apex, Queueable Apex, Scheduled Apex, and future methods): 200 method calls per full Salesforce user license or Force.com App Subscription license, per 24-hour period. Chatter Only, Customer Portal User, and Partner Portal User licenses are not counted toward this limit.