I'm trying to create a custom Link (or Button) that will open up an apex page I built and have 2 problems.

First problem

I've been trying to use the page as a Content Source as it's not listed, looking at various threads on this I have this on my page

<apex:page standardController="Booking_Sheet_Tick_Box__c" extensions="BookingSheetExtension">

Then I have an apex class BookingSheetExtension

public class BookingSheetExtension
{
	// Class variables
	...
	private final Booking_Sheet_Tick_Box__c bookingSheetObj;
	
	// Constructor	
	public BookingSheetExtension( ApexPages.StandardController controller )
	{
		this.bookingSheetObj = ( Booking_Sheet_Tick_Box__c )controller.getSubject();
		this.apiGetBookingSheet();
	}

	...

}

 I can open the page by typing in the url and it works fine. But it won't appear as a Content Source for my custom links and buttons.

Second problem

I gave up on this and just used Content Source = URL then put "/apex/My_Page?....." in the editor field. That works, to an extent, but now I can't get it to add in a value from a lookup field.

I'm adding the link to a custom object Procedure__c. In Procedure__c I have a Lookup to another custom object Procedure_Type__c (this has to be an object bttw, I can't just use a picklist)

I want the link to grab one of the fields from Procedure_Type__c for my custom link but it isn't being populated in the link

This is what I actually have in the editor field "/apex/Booking_Sheet?procedure_type_id={!Procedure_Type__c.External_Type_Id__c}"

and that opens up the page with the url "http://[salesforce.url]/apex/Booking_Sheet?procedure_type_id="

I've checked the objects that I'm using and they are all in the Procedure lookup, and they have a value for External_Type_Id__c

Does anyone have any ideas on what I could be doing wrong? I'm mostly interested in problem 2, but it would be nice to get problem 1 sorted out as well.

Thanks,

Mike