Hi Max,
I would say it gets too complicated to send SOAP requests via Seotools formulas and populating the SOAP protocol as a body. I would try to create a connector for this. You can start with one of the existing connector xml files located in the Connectors folder. Here is an example of a request you can edit to this API:
<RestConnector Id="Accounts" Title="List Accounts">
<Fetch>
<HttpSettings>
<RequestHeaders>
<Header Name="SOAPAction">FindAccountsOrCustomersInfo</Header>
</RequestHeaders>
<RequestMethod>POST</RequestMethod>
<RequestContentType>text/xml; charset=utf-8</RequestContentType>
<RequestBody>
<![CDATA[
<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
<s:Header>
<h:ApplicationToken i:nil="true" xmlns:h="https://bingads.microsoft.com/Customer/v12" xmlns:i="http://www.w3.org/2001/XMLSchema-instance"/>
<h:AuthenticationToken xmlns:h="https://bingads.microsoft.com/Customer/v12">@(Model.Authenticator.Token)</h:AuthenticationToken>
<h:DeveloperToken xmlns:h="https://bingads.microsoft.com/Customer/v12">1193759878590095</h:DeveloperToken>
</s:Header>
<s:Body>
<FindAccountsOrCustomersInfoRequest xmlns="https://bingads.microsoft.com/Customer/v12">
<Filter/>
<TopN>1000</TopN>
</FindAccountsOrCustomersInfoRequest>
</s:Body>
</s:Envelope>
]]>
</RequestBody>
</HttpSettings>
<Fetch.Url>
<![CDATA[
https://clientcenter.api.bingads.microsoft.com/Api/CustomerManagement/v12/CustomerManagementService.svc
]]>
</Fetch.Url>
</Fetch>
<Parse>
<Xpath Expr="//*[name()='accountinfowithcustomerdata']/*[name()='a:accountinfowithcustomerdata']">
<Xpath Expr="./*[name()='a:accountid']" Id="AccountId" Converter="Auto"/>
<Xpath Expr="./*[name()='a:accountname']" Id="AccountName"/>
<Xpath Expr="./*[name()='a:accountnumber']" Id="AccountNumber" Converter="Auto"/>
<Xpath Expr="./*[name()='a:accountlifecyclestatus']" Id="AccountStatus"/>
<Xpath Expr="./*[name()='a:customerid']" Id="CustomerId" Converter="Auto"/>
<Xpath Expr="./*[name()='a:customername']" Id="CustomerName"/>
</Xpath>
</Parse>
<Resource Id="Fail"/>
</RestConnector>