For transactions requests, you should enter the from and to parameters in ISO 8601 UTC format, i.e.
2018-02-18T00:00:00TZD
ISO8601 sets out an internationally agreed way to represent time & date. Find more info on ISO 8601 at this link.
TZD
It is also important to include the Time Zone Designator (TZD), (Z or +hh:mm or -hh:mm) to avoid any misinterpretations.
The + or - values indicate how far ahead or behind a time zone is from the UTC (Coordinated Universal Time) zone.
For some providers, at certain times of the year, they may return transactions from an incorrect date or time range.
This is due to differences in the standards used for time & date between TrueLayer & provider
For example, at the start of BST transactions may be returned for a day before the requested time range, if that provider uses BST instead of ISO8601 UTC.
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What is the DateTime format for a transaction request?