We just deployed an addition to Dynamic ESS for UK Octopus users: you now have the option to indicate if your Octopus price (from your API key) includes or excludes VAT.
As this differs per user, please check your Octopus contract details to see if VAT is included in your Octopus energy tariffs.
Let us know if you have any feedback on this feature.
Could it be that your price includes the VAT, but the default we put that field to is ‘off’? If you could try it for a bit with / without VAT to see if that resolves it, that’d be great.