SQS automatically converting '+' to ' '(blank) character

Question

I have an API Gateway configured to send a json message to SQS.

Below is the logs present at API Gateway end

Endpoint request body after transformations: Action=SendMessage&MessageBody=
{
    "crmData": {
        "lead_number": "+1-876-543-3210"
    }
}
&MessageGroupId=9000055557&MessageDeduplicationId=31f51711-8126-43b5-87ef-a687ab8778a4

The corresponding message received by SQS is given below:

{
  "crmData": {
    "lead_number": " 1-876-543-3210"
  }
}

As one can see that the '+' symbol in lead_number is getting replaced by a blank. Needed help in understanding what can be done to prevent such conversion, given the fact that this message is automatically getting sent from API Gateway?

Looked into documentation of both API Gateway and SQS, but couldn't find any leads.