How Target ROAS works
You give Google a return on ad spend target, and its Smart Bidding only bids into auctions where it predicts it can hit that return, adjusting each bid to maximize total conversion value. It is optimizing toward a value goal, not capping any single cost. It is the value-based sibling of Target CPA, which optimizes toward a cost per conversion instead.
It is hungry for conversion volume
Value-based bidding can only predict a return if it has enough conversions to learn from. Google recommends judging and running it over periods with meaningful volume, commonly cited as around 50 conversions in 30 days with value data. On a niche, low-volume campaign there is not enough signal, so a normal quiet week reads as failure and Google throttles delivery to protect the target, which starves it further. We unpack that death spiral, and the fix, in why your Target ROAS campaign keeps stalling out.
Changing the target restarts learning
tROAS is Smart Bidding, so editing the target is a significant edit that re-enters the learning period. Repeatedly lowering the target to revive a stalled campaign just keeps it in permanent relearning. If you cannot feed a value target honestly yet, Maximize conversions asks for no target at all and is the safer home for low volume.