Odata Post gets stuck in GW Handler

Hello,

I perform an oData Create out of an UI5 App. But it gets stuck in the service handler in the gateway.

I analysed it with a payload trace and I found out that the payload/json is alright. Because I performed the same call within the GW SAP Client and the call worked.

But from outside via browser the request also includes a metatag which is not visible in the internal call.

invalid:true

Any professional oData expert at hand?

Thx