200 Success. The body of the response return successful messages or error messages.

400 One of the query parameters is missing or not valid. One example in 400 status.

404 The URL wasn't found on the server.

500 Unexpected server error. One example in 500 status.

503 The service is temporarily unavailable.

Please check the parameters first. It might be missing the required parameters, spelling mistakes in the parameters or other reasons.

If this error message is returned even after the above error is removed when calling the API for sending emails using the SOAP protocol, check whether the email content uses HTML tags but is not escaped.
HTML tags need to be escaped. e.g. "<div>Hello</div>" is escaped to "<div>Hello</div>".

Call API by SOAP1.1 or SOAP1.2 with XML and will serialize the XML data.

The format of datetime should be the format of ISO 8601 calendar datetimes based on , YYYY-MM-DDTHH:mm:ss. Otherwise, it will returns an error.

Reference:
https://www.w3schools.com/XML/schema_dtypes_date.asp
https://stackoverflow.com/questions/254753/what-is-the-correct-format-to-use-for-date-time-in-an-xml-file

"Bad Request" is caused by an error in the format of the parameter so that cannot serialize XML in general.
The common errors, e.g. tags are not displayed in pairs, error values of parameters or other reasons.

For example, the value of parameter myFileStream in the UploadContactListFile API is not encrypted with the base64 algorithm.

When adding your values that include HTML tags to your SOAP request, replace < with <, > with > and & with &.

There are three methods to transfer array by HTTP Post:

The second type of data is correct.
Otherwise, it will return the error "System.NullReferenceException: Object reference not set to an instance of an object. ".

The value will be the first one while using the function http_build_query to generate parameters. So it cannot be used in HTTP Post.

Please find the reference in "How th call SOAP request with CURL in PHP".

First make sure the loginEmail and APIKey/password are correct, then check if the API Url for the account is correct.

How to get the API Url？

When you use the API to add subscriber, if the parameter optInType is On, then the status of the subscriber will be Unconfirmed, and it can be updated to Active using API UpdateSubscriberStatus.

optInType | UpdateSubscriberStatus

The wrong APIUrl (service.rspread.com) was requested. Modify the APIUrl according to the APIUrl of the account or the error message.
For example, the APIUrl should be modified to 'service6.rspread.net' according to this error message.

How to get the API Url？

How to get the API Url？