Azure B2C: Checking if another claim exists during local account creation - azure

Question

In addition to the usual creation of an account based on whether the e-mail used doesn't currently exist, I would like to know how I can also check if another claim value doesn't exist in Azure Active Directory.
For example, for our application, anyone who creates an account must provide an organization name. Once they signup, they are the owner of their organization group.
Before account creation, I want to check if an organization name is not associated with any other account (we're going to do sign-up via invitation if the owner wants to add people to their organization). If it doesn't exist, then create the account. Otherwise, I want to throw an error and prevent the creation of an account.
After looking through the Azure B2C technical profiles documentation, I would think that modifying AAD-UserWriteUsingLogonEmail would be my best guess.
I've tried two approaches so far. The first approach was including the input claim for the organization name. However, this just freezes the test flow:
<TechnicalProfile Id="AAD-UserWriteUsingLogonEmail">
<Metadata>
<Item Key="Operation">Write</Item>
<Item Key="RaiseErrorIfClaimsPrincipalAlreadyExists">true</Item>
</Metadata>
<IncludeInSso>false</IncludeInSso>
<InputClaims>
<InputClaim ClaimTypeReferenceId="email" PartnerClaimType="signInNames.emailAddress" Required="true" />
<InputClaim ClaimTypeReferenceId="extension_organizationName" Required="true" />
</InputClaims>
<PersistedClaims>
<!-- Required claims -->
<PersistedClaim ClaimTypeReferenceId="email" PartnerClaimType="signInNames.emailAddress" />
<PersistedClaim ClaimTypeReferenceId="newPassword" PartnerClaimType="password"/>
<PersistedClaim ClaimTypeReferenceId="displayName" DefaultValue="unknown" />
<PersistedClaim ClaimTypeReferenceId="passwordPolicies" DefaultValue="DisablePasswordExpiration" />
<!-- Optional claims. -->
<PersistedClaim ClaimTypeReferenceId="givenName" />
<PersistedClaim ClaimTypeReferenceId="surname" />
<PersistedClaim ClaimTypeReferenceId="extension_organizationName" />
</PersistedClaims>
<OutputClaims>
<OutputClaim ClaimTypeReferenceId="objectId" />
<OutputClaim ClaimTypeReferenceId="newUser" PartnerClaimType="newClaimsPrincipalCreated" />
<OutputClaim ClaimTypeReferenceId="authenticationSource" DefaultValue="localAccountAuthentication" />
<OutputClaim ClaimTypeReferenceId="userPrincipalName" />
<OutputClaim ClaimTypeReferenceId="signInNames.emailAddress" />
</OutputClaims>
<IncludeTechnicalProfile ReferenceId="AAD-Common" />
<UseTechnicalProfileForSessionManagement ReferenceId="SM-AAD" />
</TechnicalProfile>
The second approach was something similar, but instead using an <InputClaimsTransformations> to check if an organization name exists via the DoesClaimExist action. When using this approach, I get the following error:
Unable to validate the information provided.
Since I'm new to creating custom policies, is modifying the AAD-UserWriteUsingLogonEmail profile on the right track or do I need a completely different approach?
EDIT:
After following Barbara's links, I was able to get the validation working. However, I'm still having issues trying to prevent an account that is using an organization that is already associated with another account. It seems that using an <InputClaimsTransformations> doesn't really do anything.

Answer 1

The error message Unable to validate the information provided. indicates that you did not configure your custom policy correctly to be able to use custom claims.
Thus you have to follow the documentation:
Get the application properties of the extensions app
Modify your custom policy to include the application properties in the AAD-Common-technical profile
Please follow the steps and try again.