Router contract always throws gas estimate error

Describe the bug When trying to add liquidity to a token pair, the following error constantly pops up:

Gas estimation errored with the following message (see below). The transaction execution will likely fail. Do you want to force sending? Internal JSON-RPC error. { "code": -32000, "message": "gas required exceeds allowance (11000000)" }

To Reproduce Steps to reproduce the behavior:

Open Remix
Import the flattened NiiFi Router contract.
Compile the NiiFi Router contract with the Optimism Remix compiler plugin with version 0.6.12 of Solidity.
Connect to the Nahmii testnet in Remix. Make sure your wallet contains testnet ETH and KNII. (or whatever token you test)
Select the IUniswapRouter02 contract in the deployment interface.
Attach the interface to address 0x31965F4782743be64CD3868f4Bc6843b82273feB with the at address button.
Use any of the addLiquidity functions. Example arguments for the KNII-ETH pair: tokenA: 0xB68553758df8c253746d3cED96aA1De896F09470 (KNII, 6 decimals) tokenB: 0x4200000000000000000000000000000000000006 (wETH, 28 decimals) amountADesired: 5000000000 amountBDesired: 2000000000000000000 amountAMin: 4000000000 amountBMin: 1000000000000000000 to: Your address deadline: Current unix timestamp + 100000

Expected behavior The function should successfully execute and add liquidity to the given tokens token pair.

Additional context Smart contract addresses:

Router address: 0x31965F4782743be64CD3868f4Bc6843b82273feB
Factory address: 0x238AE0a8bDFf3d03B328Af85fD7fdf570Fee8819
KNII address: 0xB68553758df8c253746d3cED96aA1De896F09470
NEURO address: 0xB59C984a529490fde6698702342b292840743bb8
KNII-NEURO pair: 0x144060d957843F22FCF80b4a0aeC227f9152EA47
KNII-ETH pair: 0x69B15D61ee8cBe07408ca55819e57bC4B4E13Db5
NEURO-ETH pair: 0x1671511FDE3Fa5191858049C1Bd8B4a99CA306cb

Tried and tested

Factory, Router and personal addresses have been whitelisted.
Was able to execute functions on the Factory, not on the Router.
Router has been granted approval for the mentioned tokens. (ETH, KNII, NEURO)
Tested logic related to block.timestamp, doesn't seem to be the issue.
Contract variables hold the correct data.
Pair data is correct according to the Factory contract.
Issue is not related to wrong nonces.

Potential next steps

Deploy an unoptimized set of Factory-Router contracts and verify them on Blockscout, in the hope that Blockscout will provide some more details on why force-pushed transactions fail.
Enable arbitrary deployments to see whether it's a permissions issue.

nahmii / niifi-token-contract

Router contract always throws gas estimate error #1