Use PSI to add the LocalCustomField Text1 to Project

Hello.

Iam using the PSI to read and update local CustomFields like Text1, Text2, Flag1, ...

For example I found Text1 by using the GUID 00039b7-8bbe-4ceb-82c4-fa8c0b400033

Everything works fine but Iam not able to add these fields to new Projects. I always get the error: CustomFieldInvalidUid

So I can read and update Text1 but Iam not able to add this field to new Projects.

Isn't it possible with PSI?

Thanks for your help and best regards,

Timo