Error when trying to call service via AppToAppSSO destination

Hello,I am trying to configure AppToAppSSO with external IdP on HCP. Our hana db version is 1.00.122.12.1502962396.

XS admin part is configured and destination is added in the UI app.

When I call XS app I get that error:

HTTP Status 400 - Service Provider endpoint saml2/sp/acs could not redirect to original application URL because it could not convert the received RelayState to original application URL.

When I call HTM5 app I get that error:

StatusCode in ResponseMessage != OK; please refer to the database trace for more information

Xsengine trace

[6097]{6097}[-1/-1] 2017-12-01 19:36:05.264552 e XSSession XSSessionLifecycle.cpp(00341) : Assertion authentication for user failed with reason: Unable to verify XML signature(StatusCode: , StatusMessage: )<br>[6097]{6097}[-1/-1] 2017-12-01 19:36:05.265197 e XSRequestHandler RequestHandler.cpp(00808) : exception 1: no.1000090 (HttpClient/Web/WebEntityBase.h:78)<br> Reached unreachable code

I don't know how to fix that error.

I followed this blog and checked that question but this doesn't give me an answer how I should proceed.

Thanks,

Lazar Hristov