Near the end of the first island there will be an opportunity to use 30 Tax Tokens to build a bridge to the next area. After shooting 30 tokens in the achievement should pop. This is the only bridge that will pop the achievement, so if it did not work you will have to do the following:
-Finish the rest of the game (optional but HIGHLY RECOMMENDED)
-once you have gotten all the other achievements, go to the main menu, then go to Options > General > Delete Save Data.
THIS WILL DELETE ALL PROGRESS SO PROCEED WITH CAUTION.
-Go back to Level Select and play the first island over again.
This is what I had to do to pop it. It's a little tedious but it worked the second time.
I would recommend getting happiness to 100% in the area with the bridge builder, make sure all the goop is cleared off of the power unit and builder, and finally, shoot all 30 tokens at once.
My first try I only brought like 20 tokens so i shot those in and went back for 10 more, I cannot confirm this caused it not to unlock, but I would avoid splitting the tokens at all costs to be safe.