In fact I have reserved the book but as I had lost my password, I could not pay
Are the tenses used correctly I have a little doubt on past perfect had lost
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Sign up to join this communityThe answer is that it depends.
If you have subsequently recovered your passport, the PAST PERFECT fits. (You had lost it but you have since found it.)
If you have not yet recovered your passport, you could use the PRESENT PERFECT. (It is still lost.)
In practice, many native English speakers would also use the PAST TENSE. But either the PAST PERFECT or PRESENT PERFECT is a nicer choice, depending on the context.