Problem setting up a static IP address

[RobLatour]

I am having problems setting up a static IP address for a connected device under Services: DHCPv4: [LAN].

My configuration (all connected via LAN cables) is as follows:
 
ISP (bridging to) ->
opnsense box ->
tp-link Archer A10 WiFi Router setup as an access point ->
Dlink 8-Port Gigabit Easy Unmanaged Desktop Switch GO-SW-8G ->
the connected device.

Under Services: DHCPv4: [LAN]
under DHCP Static Mappings for this interface.
I am trying to set-up and address of 192.168.1.12

However, the device always seems to connect to 192.168.1.128 - even after being powered down and up again, and even with the Dlink switch being powered down and up again.

However, two other devices, both connected directly to the TP Link access point, do have their IP addresses statically set and working fine to 192.168.1.10 and 192.168.1.11 (as setup up under Services: DHCPv4: [LAN], under DHCP Static Mappings).

So I'm wondering, does the fact that I am using an unmanaged switch between the device and the access point mean that I can't set static IP addresses to anything that it connects?

I have triple-checked I am using the right mac address for the connected device.

UPDATE: I have now plugged the device in question directly into the TP-Link Access Point, cutting the DLink switch out of the equation, however still no love - the device stubbornly stays addressed at 192.168.1.128.

Thanks in advance for your help.

[RobLatour]

SOLVED

so, it turned out to be the connected device itself, a Raspberry PI running Pihole and CUPS (Print Server).

needed to Putty in to the device and issue the command:
pihole -r
and then reconfigure the setup; specifying the IP address that I wanted it to be.

for more info see here: https://www.reddit.com/r/pihole/comments/epkba4/cant_change_the_ip_address_of_the_pihole/