MIDIPortConnectSource() returning -50 error code

The following is a minimal working example of my code. Some of the print statement output the status of a CoreMIDI function. Every one of these CoreMIDI methods works properly, except for MIDIInputConnectSource(), which outputs -50. Please scroll to the end to see the output.

        // Set up client
        var client = MIDIClientRef()
        var status: OSStatus = MIDIClientCreateWithBlock("MIDI Client" as CFString, &client) { _ in }
        print("MIDIClientCreateWithBlock >>", String(describing: status))

        // Set up port
        var port = MIDIPortRef()

        // List sources
        let numSources = MIDIGetNumberOfSources()
        print("\(numSources) sources found")
        for i in 0..<numSources {
            let source = MIDIGetSource(i)
            var sourceName: Unmanaged<CFString>?
            status = MIDIObjectGetStringProperty(source, kMIDIPropertyName, &sourceName)
            print("MIDIObjectGetStringProperty >>", String(describing: status))
            print("Name of source \(i): \(sourceName?.takeRetainedValue() as String?)")
        }

        
        // Choose source
        var source: MIDIEndpointRef = MIDIGetSource(0)        

        // Connect port to source
        status = MIDIPortConnectSource(port, source, &source)
        print("port:", port)
        print("source:", source)
        print("client:", client)
        print("MIDIPortConnectSource >>", String(describing: status))

        var count = 0

        status = MIDIInputPortCreateWithProtocol(
                client,
                "Destination Name" as CFString,
                MIDIProtocolID._1_0,
                &port) { _, _ in

            count += 1
            print("MIDI event(s) received.")
        }

        print("MIDIInputPortCreateWithProtocol >>", String(describing: status))

Output of code above:

MIDIClientCreateWithBlock >> 0
1 sources found
MIDIObjectGetStringProperty >> 0
Name of source 0: Optional("iRig Keys")
port: 0
source: 102203411
client: 102203464
MIDIPortConnectSource >> -50
MIDIInputPortCreateWithProtocol >> 0