Change Encoding on WCF Adapter

It seems that ISO-8859-1 encoding is not supported in the WCF-BasicHttp adapter in BizTalk. So you could try using the WCF-Custom adapter as the Transport Type, and in the Binding tab in the Transport Properties window, select customBinding as the Binding Type, then, under the Binding panel, click on the textMessageEncoding extension to bring up its properties (in the Configuration panel), and enter ISO-8859-1 as the value for the field writeEncoding.