Hi all,
I created a custom button in Classic by hand:

It shows in Metadata API just fine.

Replicating the same thing with Metadata API (with help from IntelliJ + Illuminated Cloud) with:

<?xml version="1.0" encoding="UTF-8"?>
<WebLink xmlns="http://soap.sforce.com/2006/04/metadata">
    <availability>online</availability>
    <displayType>button</displayType>
    <encodingKey>UTF-8</encodingKey>
    <linkType>page</linkType>
    <masterLabel>FSM_BrianPlaying2</masterLabel>
    <openType>newWindow</openType>
    <page>FSM_ServiceAppointmentDoW</page>
    <position>none</position>
    <protected>false</protected>
    <showsLocation>false</showsLocation>
    <showsStatus>false</showsStatus>
    <fullName>ServiceAppointment.FSM_BrianPlaying2</fullName>
</WebLink>

Then the deployment goes fine, but the button is "nowhere" to be seen.
However, with a bit of SOQL, it turns out that it is there, but on the wrong type.

Any ideas on how to fix this?

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Error is following...


"There was an unhandled exception. Please reference ID: GXDUIIXP. Error: Faraday::ClientError. Message: INVALID_TYPE: SELECT Title FROM Knowledge__kav Where PublishStatus ^ ERROR at Row:1:Column:19 sObject type 'Knowledge__kav' is not supported. If you are attempting to use a custom object, be sure to append the '__c' after the entity name. Please reference your WSDL or the describe call for the appropriate names."